This application is a national stage of PCT/EP 98/01411 filed Jul. 1, 1998 and based upon French application 97 08 546 filed Jul. 1, 1997 under the International Convention.
The present invention defines devices and procedures to be included in radiotelephones and in their environment in order to allow them to react correctly to cases of jamming and of filtering.
Radiotelephones, which are becoming more and more widespread, have the drawback* of creating an audible nuisance. The current solutions, such as the use of vibrators, solve the problem only incompletely since they assume a deliberate act by the users and are inoperative in the event of forgetfulness or of unwillingness. In order to limit this nuisance, apparatus for filtering and neutralizing portable radiotelephones will be installed in places to be protected: cinemas, trains, etc. Some of this filtering apparatus is described by the patents FR 97 07000, FR 97 10105 and PCT FR 98/01109, and is designated by the term xe2x80x9cjammerxe2x80x9d.
In the texts below we will use the terms filtering and jamming equivalently, whether they are deliberate or accidental, or result from shadow areas.